An understanding of biological oxidations is fundamental to an understanding of heart functions. The energy produced in biological oxidations is used to drive the synthesis of adenosine triphosphate (ATP), which is the major energy source for heart muscle contraction and active ion transport. The objective of this research is to discern the significance of sulfur chemistry in biological oxidation. The oxidation of divalent sulfides is surprisingly facile in the presence of suitable neighboring groups, such as those commonly found in proteins. Neighboring group interaction depends markedly on geometry. Simple rigid systems are studied to discern the basis for the interactions. A series of physical organic, electrochemical, spectroscopic (IR, UV, ESR and PE), X-ray crystallographic and pulse radiolysis techniques are used to study electron deficient sulfide intermediates. A sulfur atom is ligated to the iron atom of cytochrome c and analogues. The significance of the iron-sulfur interaction will be studied. The combination of neighboring group interactions between the ligated sulfur atom and the proximate side chains of other amino acids and heme iron-sulfur interactions may be the key to understanding the redox properties of these cytochromes. Our work on the chemistry of electron deficient sulfides also offers the opportunity to discern the mechanism and significance of the reaction of hydroxyl radicals with methional. Hydroxyl radicals are very important intermediates in biological oxidations and methional has been widely used as a specific probe for these radicals in enzymic systems.